1. Field of Endeavor
The present invention relates to electrode arrays and more particularly to high density polymer-based integrated electrode arrays.
2. State of Technology
U.S. Pat. No. 4,573,481 for an implantable electrode array by Leo A. Bullara, patented Mar. 4, 1986 provides the following background information, “It has been known for almost 200 years that muscle contraction can be controlled by applying an electrical stimulus to the associated nerves. Practical long-term application of this knowledge, however, was not possible until the relatively recent development of totally implantable miniature electronic circuits which avoid the risk of infection at the sites of percutaneous connecting wires. A well-known example of this modern technology is the artificial cardiac pacemaker which has been successfully implanted in many patients. Modern circuitry enables wireless control of implanted devices by wireless telemetry communication between external and internal circuits. That is, external controls can be used to command implanted nerve stimulators to regain muscle control in injured limbs, to control bladder and sphincter function, to alleviate pain and hypertension, and to restore proper function to many other portions of an impaired or injured nerve-muscle system. To provide an electrical connection to the peripheral nerve which controls the muscles of interest, an electrode (and sometimes an array of multiple electrodes) is secured to and around the nerve bundle. A wire or cable from the electrode is in turn connected to the implanted package of circuitry.”
U.S. Pat. No. 6,052,624 for a directional programming for implantable electrode arrays by Carla M. Mann, patented Apr. 18, 2000 provides the following background information, “Within the past several years, rapid advances have been made in medical devices and apparatus for controlling chronic intractable pain. One such apparatus involves the implantation of an electrode array within the body to electrically stimulate the area of the spinal cord that conducts electrochemical signals to and from the pain site. The stimulation creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient. One theory of the mechanism of action of electrical stimulation of the spinal cord for pain relief is the “gate control theory.” This theory suggests that by simulating cells wherein the cell activity counters the conduction of the pain signal along the path to the brain, the pain signal can be blocked from passage. Spinal cord stimulator and other implantable tissue stimulator systems come in two general types: “RF” controlled and fully implanted. The type commonly referred to as an “RF” system includes an external transmitter inductively coupled via an electromagnetic link to an implanted receiver that is connected to a lead with one or more electrodes for stimulating the tissue. The power source, e.g., a battery, for powering the implanted receiver-stimulator as well as the control circuitry to command the implant is maintained in the external unit, a hand-held sized device that is typically worn on the patient's belt or carried in a pocket. The data/power signals are transcutaneously coupled from a cable-connected transmission coil placed over the implanted receiver-stimulator device. The implanted receiver-stimulator device receives the signal and generates the stimulation. The external device usually has some patient control over selected stimulating parameters, and can be programmed from a physician programming system.”
U.S. Pat. No. 6,230,057 for a multi-phasic microphotodiode retinal implant and adaptive imaging retinal stimulation system by Vincent Chow and Alan Chow, patented May 8, 2001 and assigned to Optobionics Corporation provides the following background information, “A variety of retinal diseases cause vision loss or blindness by destruction of the vascular layers of the eye including the choroid, choriocapillaris, and the outer retinal layers including Bruch's membrane and retinal pigment epithelium. Loss of these layers is followed by degeneration of the outer portion of the inner retina beginning with the photoreceptor layer. Variable sparing of the remaining inner retina composed of the outer nuclear, outer plexiform, inner nuclear, inner plexiform, ganglion cell and nerve fiber layers, may occur. The sparing of the inner retina allows electrical stimulation of this structure to produce sensations of light. Prior efforts to produce vision by electrically stimulating various portions of the retina have been reported. One such attempt involved an externally powered photosensitive device with its photoactive surface and electrode surfaces on opposite sides. The device theoretically would stimulate the nerve fiber layer via direct placement upon this layer from the vitreous body side. The success of this device is unlikely due to it having to duplicate the complex frequency modulated neural signals of the nerve fiber layer. Furthermore, the nerve fiber layer runs in a general radial course with many layers of overlapping fibers from different portions of the retina. Selection of appropriate nerve fibers to stimulate to produce formed vision would be extremely difficult, if not impossible. Another device involved a unit consisting of a supporting base onto which a photosensitive material such as selenium was coated. This device was designed to be inserted through an external scleral incision made at the posterior pole and would rest between the sclera and choroid, or between the choroid and retina. Light would cause a potential to develop on the photosensitive surface producing ions that would then theoretically migrate into the retina causing stimulation. However, because that device had no discrete surface structure to restrict the directional flow of charges, lateral migration and diffusion of charges would occur thereby preventing any acceptable resolution capability. Placement of that device between the sclera and choroid would also result in blockage of discrete ion migration to the photoreceptor and inner retinal layers. That was due to the presence of the choroid, choriocapillaris, Bruch's membrane and the retinal pigment epithelial layer all of which would block passage of those ions. Placement of the device between the choroid and the retina would still interpose Bruch's membrane and the retinal pigment epithelial layer in the pathway of discrete ion migration. As that device would be inserted into or through the highly vascular choroid of the posterior pole, subchoroidal, intraretinal and intraorbital hemorrhage would likely result along with disruption of blood flow to the posterior pole. One such device was reportedly constructed and implanted into a patient's eye resulting in light perception but not formed imagery. A photovoltaic device artificial retina was also disclosed in U.S. Pat. No. 5,024,223. That device was inserted into the potential space within the retina itself. That space, called the subretinal space, is located between the outer and inner layers of the retina. The device was comprised of a plurality of so-called Surface Electrode Microphotodiodes (“SEMCPs”) deposited on a single silicon crystal substrate. SEMCPs transduced light into small electric currents that stimulated overlying and surrounding inner retinal cells. Due to the solid substrate nature of the SEMCPs, blockage of nutrients from the choroid to the inner retina occurred. Even with fenestrations of various geometries, permeation of oxygen and biological substances was not optimal. Another method for a photovoltaic artificial retina device was reported in U.S. Pat. No. 5,397,350, which is incorporated herein by reference. That device was comprised of a plurality of so-called Independent Surface Electrode Microphotodiodes (ISEMCPs), disposed within a liquid vehicle, also for placement into the subretinal space of the eye. Because of the open spaces between adjacent ISEMCPs, nutrients and oxygen flowed from the outer retina into the inner retinal layers nourishing those layers. In another embodiment of that device, each ISEMCP included an electrical capacitor layer and was called an ISEMCP-C. ISEMCP-Cs produced a limited opposite direction electrical current in darkness compared to in the light, to induce visual sensations more effectively, and to prevent electrolysis damage to the retina due to prolonged monophasic electrical current stimulation. These previous devices (SEMCPs, ISEMCPs, and ISEMCP-Cs) depended upon light in the visual environment to power them. The ability of these devices to function in continuous low light environments was, therefore, limited. Alignment of ISEMCPs and ISEMCP-Cs in the subretinal space so that they would all face incident light was also difficult.”
U.S. Pat. No. 6,324,429 for a chronically implantable retinal prosthesis by Doug Shire, Joseph Rizzo, and John Wyatt, of the Massachusetts Eye and Ear Infirmary Massachusetts Institute of Technology issued Nov. 27, 2001 provides the following information, “In the human eye, the ganglion cell layer of the retina becomes a monolayer at a distance of 2.5–2.75 mm from the foveal center. Since the cells are no longer stacked in this outer region, this is the preferred location for stimulation with an epiretinal electrode array. The feasibility of a visual prosthesis operating on such a principle has been demonstrated by Humayun, et al. in an experiment in which the retinas of patients with retinitis pigmentosa, age-related macular degeneration, or similar degenerative diseases of the eye were stimulated using bundles of insulated platinum wire. The patients were under local anesthesia, and they described seeing points of light which correctly corresponded with the region of the retina in which the stimulus was applied (Humayun, M., et al., Archiv. Ophthalmol., 114: 40–46, 1996). The form of the stimulating device was, however, not suited for chronic implantation. The threshold for perception was reported to be in the range of 0.16–70 mC/cm.sup.2. This confirmed the results of earlier experiments on animal subjects by the instant inventors and others which indicated that strong evoked cortical potentials could be observed when rabbit retinas were stimulated using passive microfabricated electrode arrays similar in some respects to the ones proposed in the current invention (Rizzo, J. F., et al., ARVO Poster Session Abstract, Investigative Ophthalmology and Visual Science, 37: S707, 1996; Walter, P., et al. Investigative Ophthalmology and Visual Science, 39: S990, 1998). The instant inventors have, with others, performed three surgical procedures using microfabricated electrode arrays and similar in technique to those described by Humayun and confirmed that a consistent response to input electrical stimuli could be noted by the patient. The task of creating a retinal implant has been addressed by Chow, in U.S. Pat. No. 5,016,633, who proposed a subretinal implant based on a microphotodiode array. The procedure involved in its implantation is so biologically intrusive, however, that successful implementation of such a device in human subjects has not been reported. Furthermore, an entirely passive array will be rather insensitive under normal lighting conditions, and an array powered from outside the body by means of a direct electrical connection will likely lead to infections and again, be so intrusive as to be objectionable. Earlier designs of the present inventors placed all components of the prosthesis on the retinal surface (U.S. patent application Ser. No. 19/074,196, filed May 7, 1998, and U.S. Pat. No. 5,800,530, both of which are incorporated herein by reference). It became quickly apparent that the delicate retina could not withstand the mechanical burden which was at least partially the result of the relatively thick profile of the microelectronic components. A later prototype included one significant change in design—the bulky microelectronic components were moved anteriorly within the eye, off of the retinal surface. In this configuration, the microelectronics are held in a custom-designed intraocular lens, and only a thin ribbon containing the microelectrodes extends rearwardly to the retinal surface.”